1. Field of the Invention
The present invention relates to a relay abnormality detecting device for detecting an abnormality in relays for driving a motor such as an automotive door lock motor, an automotive power window motor, and an automotive sun roof motor.
2. Description of the Prior Art
In the past, forward and backward rotations of a motor such as an automotive door lock motor have been controlled by a circuit as shown in FIG. 5, for example.
Referring to FIG. 5, when a forward or backward rotation command is applied to a controller 1 including an ECU by actuation of an input portion SW including a switch, a switching control signal output terminal O1 or O2 of the controller 1 outputs a high-level (referred to as "H" hereinafter) switching control signal to a base of an first NPN transistor Q1 serving as a switching element for forward rotation or to a base of a second NPN transistor Q2 serving as a switching element for backward rotation, to turn on the transistor Q1 or Q2. When the transistor Q1 turns on, current flows from a battery +B serving as a power supply through a fuse F2 to a relay coil C1 of a first motor driving relay RL1 to excite the relay coil C1. Then a c-contact T1 of the first relay RL1 is switched from a normally-closed terminal to a normally-open terminal. Likewise, when the transistor Q2 turns on, current flows from the battery +B through the fuse F2 to a relay coil C2 of a second motor driving relay RL2 to excite the relay coil C2. Then a c-contact T2 of the second relay RL2 is switched from a normally-closed terminal to a normally-open terminal.
At this time, a motor driving portion 2 for driving a motor M is formed by the transistors Q1, Q2, and the relays RL1, RL2.
Switching of the c-contact T1 to the normally-open terminal by excitation of the first relay RL1 causes current from the battery +B to flow to a ground through a fuse F1, the normally-open terminal and a common terminal of the c-contact T1 of the first relay RL1, the motor M, and a common terminal and the normally-closed terminal of the c-contact T2 of the second relay RL2. The current flows through the motor M in a direction of forward rotation to forwardly rotate the motor M.
On the other hand, switching of the c-contact T2 to the normally-open terminal by excitation of the second relay RL2 causes current from the battery +B to flow to a ground through the fuse F2, the normally-open terminal and a common terminal of the c-contact T2 of the second relay RL2, the motor M, and a common terminal and the normally-closed terminal of the c-contact T1 of the first relay RL1. The current flows through the motor M in a direction of backward rotation to backwardly rotate the motor M.
In such a construction, if an abnormal current flows through a motor M resulting from melting of relays RL1, RL2, the fuses F1 and F2 burn and a current-flow path to the motor M is interrupted. This prevents damages to the motor M but requires replacement of the burnt fuses F1, F2 for restoration.
Hence, an arrangement of FIG. 6 is considered to interrupt the current-flow path to the motor M.
Referring to FIG. 6, when a forward or backward rotation command is applied to the controller 1 including an ECU by actuation of the input portion SW including a switch, the switching control signal output terminal O1 or O2 of the controller 1 outputs an "H" switching control signal to the base of the first NPN transistor Q1 serving as the switching element for forward rotation or to the base of the second NPN transistor Q2 serving as the switching element for backward rotation, to turn on the transistor Q1 or Q2. When the first transistor Q1 turns on, current flows from the battery +B to the relay coil C1 of the first motor driving relay RL1 to excite the relay coil C1. Then the c-contact T1 of the first relay RL1 is switched from the normally-closed terminal to the normally-open terminal. Likewise, when the second transistor Q2 turns on, current flows from the battery +B to the relay coil C2 of the second motor driving relay RL2 to excite the relay coil C2. Then the c-contact T2 of the second relay RL2 is switched from the normally-closed terminal to the normally-open terminal.
At this time, the motor driving portion 2 for driving the motor M is formed by the transistors Q1, Q2 and the relays RL1, RL2.
Switching of the c-contact T1 to the normally-open terminal by excitation of the first relay RL1 causes current from the battery +B to flow to the ground through the normally-open terminal and common terminal of the c-contact T1 of the first relay RL1, the motor M, and the common terminal and normally-closed terminal of the c-contact T2 of the second relay RL2. The current flows through the motor M in the direction of forward rotation to forwardly rotate the motor M.
Switching of the c-contact T2 to the normally-open terminal by excitation of the second relay RL2 causes current from the battery +B to flow to the ground through the normally-open terminal and common terminal of the c-contact T2 of the second relay RL2, the motor M, and the common terminal and normally-closed terminal of the c-contact T1 of the second relay RL1. The current flows though the motor M in the direction of backward rotation to backwardly rotate the motor M.
With continued reference to FIG. 6, opposite ends of the motor M are connected to detection signal input terminals I1 and I2 of the controller 1 through diodes D1 and D2, respectively. The input terminals I1 and I2 are grounded through pull-down resistors R1 and R2, respectively. The diodes D1, D2 and the resistors R1, R2 form a signal detecting portion 3. When the motor M correctly rotates in the forward direction, current from the battery +B flows to the ground through the normally-open terminal and common terminal of the c-contact T1 of the first relay RL1, an anode and a cathode of the diode D1, and the resistor R1. Then, voltage across the resistor R1 is applied to the input terminal I1 of the controller 1 in the form of an "H" detection signal, and a current flow in the direction of forward rotation is detected.
When the motor M correctly rotates in the backward direction, current from the battery +B flows to the ground through the normally-open terminal and common terminal of the c-contact T2 of the second relay RL2, an anode and a cathode of the diode D2, and the resistor R2. Then, voltage across the resistor R2 is applied to the input terminal I2 of the controller 1 in the form of an "H" detection signal, and a current flow in the direction of backward rotation is detected.
A third relay RL3 for interrupting the power supply is formed in a current-flow path between the battery +B and the motor M so as to prevent damages to the motor M when current keeps flowing through the motor M after the excitation of the relays RL1 and RL2 is released because of the occurrence of an abnormality such as melting of the relays RL1 and RL2. A cutoff control signal at a low level (referred to as "L" hereinafter) from a cutoff control signal output terminal O3 of the controller 1 causes a third NPN transistor Q3 to be switched from on to off, which in turn interrupts a current flow from the battery +B to a relay coil C3 of the third relay RL3 to turn off a relay contact T3. The turning off of the relay contact T3 interrupts the current-flow path from the battery +B to the motor M to force the motor M to stop.
Such operation will be described briefly with reference to timing charts of FIGS. 7A to 7F. When the output terminal O1 of the controller 1 goes high as shown in FIG. 7A, current is passed through the motor M in the direction of forward rotation to forwardly rotate the motor M as shown in FIG. 7F. At this time, the input terminal I1 of the controller 1 goes high as shown in FIG. 7C. A current flow through the motor M in the direction of forward rotation is detected.
On the other hand, when the output terminal O2 of the controller 1 goes high as shown in FIG. 7B, current is passed through the motor M in the direction of backward rotation to backwardly rotate the motor M as shown in FIG. 7F. At this time, the input terminal I2 of the controller 1 goes high as shown in FIG. 7D. A current flow through the motor M in the direction of backward rotation is detected.
During the correct forward and backward rotations of the motor M, the output terminal O3 of the controller 1 is held high as shown in FIG. 7E and the third relay RL3 is kept excited to hold the relay contact T3 in its on state. For instance, if current in the direction of forward rotation keeps flowing through the motor M and the motor M continues rotating in the forward direction as shown in FIG. 7F after the output terminal O1 of the controller 1 is switched from H to L as shown in FIG. 7A because of the occurrence of an abnormality such as melting of the first relay RL1, the continuous application of the "H" signal to the input terminal I1 as shown in FIG. 7C permits the controller 1 to immediately detect the abnormality occurrence in the first relay RL1, and then the output terminal O3 is changed to L as shown in FIG. 7E. This releases the excitation of the third relay RL3 to turn off the relay contact T3. Thus current through the motor M is interrupted and the motor M is forced to stop as shown in FIG. 7F.
In the above stated arrangement, however, the transistor Q3 and the third relay RL3 are required to force the motor M to stop when the motor driving relays RL1 and RL2 are abnormal. This has added to the number of components, complexity of construction, and costs.